Fixed displacement compressors

ABSTRACT

A fixed displacement compressor includes a cylinder block having a plurality of cylinder bores formed therethrough, a drive shaft rotatably supported by the cylinder block, and a plate rotatably mounted on the drive shaft. Moreover, an inclination angle of the plate varies relative to a radial line perpendicular to the drive shaft. The compressor also includes a spring positioned adjacent to the plate. The spring is adapted to urge the plate in a direction which reduces the inclination angle of the plate. In an embodiment, the plate is a swash plate. In another embodiment, the compressor further includes a cam rotor fixed to the drive shaft. In this latter embodiment, the spring is positioned between the cam rotor the plate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates generally to fixed displacement compressorsused in automotive air conditioning systems. More particularly, theinvention relates to swash plate-type, fixed displacement compressorsused in automotive air conditioning systems.

[0003] 2. Description of Related Art

[0004] A known swash plate-type, fixed displacement compressor maycomprise a cylinder block, a front housing, a valve plate, and acylinder head. The cylinder block may be substantially cylindrical andalso may be enclosed by the front housing and the cylinder head. A crankchamber may be formed between the cylinder block and the front housing.Moreover, a suction chamber and a discharge chamber may be formed withinthe cylinder head and adjacent to the valve plate. An inlet port and anoutlet port may communicate with the suction chamber and the dischargechamber, respectively, and the inlet port and the outlet port may beconnected to a refrigerant circuit of an air conditioning system of avehicle. The cylinder block, the front housing, the valve plate, and thecylinder head may be fixably attached to each other by a plurality ofbolts. Such known compressors also may comprise a plurality of cylinderbores formed in the cylinder block. The cylinder bores may be arrangedradially with respect to a central axis of the cylinder block.

[0005] Such known compressors further may comprise a drive shaft, a camrotor, a swash plate, a plurality of shoes, and a plurality of pistons.The drive shaft may extend along a central axis of such knowncompressors through the crank chamber, and also may be rotatablysupported by the front housing and the cylinder block via a pair ofbearings mounted in the front housing and the cylinder block,respectively. Such known compressors also may comprise anelectromagnetic clutch. A drive belt may be used to engage theelectromagnetic clutch by transmitting a driving force from a crankshaftof an engine of a vehicle to the electromagnetic clutch. When theelectromagnetic clutch is engaged, the driving force also is transmittedfrom the electromagnetic clutch to the drive shaft. Moreover, the camrotor may be fixed to the drive shaft and may be positioned within thecrank chamber, and a slot may be formed through the cam rotor. The swashplate also may be positioned within the crank chamber and may be fixablymounted on the drive shaft. The swash plate may comprise a pin memberwhich may extend toward the cam rotor. The pin member may be insertedinto the slot of the cam rotor.

[0006] Moreover, each piston may be positioned within a correspondingcylinder bore, and the pistons may reciprocate independently withintheir corresponding cylinder bore. Each of the pistons also may beconnected to the swash plate via a pair of shoes. Specifically, eachshoe may comprise a substantially flat surface and a substantiallysemispherical portion. The flat surface may be in slidable contact withthe swash plate, and the semispherical portion may rotatably engage asubstantially semispherical cavity of the piston. A plurality of suctionports and a plurality of discharge ports may be formed through the valveplate for each of the cylinder bores. A suction reed valve may bepositioned between the cylinder block and the valve plate. The suctionreed valve may open and may close the suction port in order to control aflow of a refrigerant from the suction chamber to the cylinder bores. Adischarge reed valve may be positioned between the valve plate and thecylinder head. The discharge reed valve may open and may close thedischarge port in order to control a flow of the refrigerant from thecylinder bores to the discharge chamber.

[0007] In operation, when the electromagnetic clutch and the drive shaftare engaged, the driving force from the engine of the vehicle istransmitted to the drive shaft, such that the drive shaft, the camrotor, and the swash plate rotate substantially simultaneously about anaxis of the drive shaft. Specifically, the rotational movement of thedrive shaft is transmitted to the cam rotor, and the rotational movementof the cam rotor is transmitted to the swash plate via a couplingmechanism comprising the slot and the pin member, such that the swashplate moves back and forth in a wobbling motion. Consequently, eachpiston reciprocates within its corresponding bore. When the pistonsreciprocate within their corresponding cylinder bore, refrigerant gasintroduced into the suction chamber via the inlet port may be drawn intoeach cylinder bore and subsequently may be compressed. When therefrigerant gas is compressed, the discharge reed valve opens and therefrigerant gas is discharged from the cylinder bores into the dischargechamber. Moreover, the refrigerant gas is discharged from the dischargechamber into the refrigerant circuit via the outlet port.

[0008] In such known compressors, the electromagnetic clutch and thedrive shaft may be engaged or disengaged in order to control the airconditioning system of the vehicle. Nevertheless, when the operation ofsuch known compressors begins, frictional forces may exist between theswash plate and the shoes. Moreover, an initial torque of the compressormay be such that the vehicle's speed may decrease when the operation ofsuch known compressors begins. Other known compressors may include anelectromagnetic clutch adapted to absorb a greater initial torque thanthe known compressors described above. However, such an electromagneticclutch may increase the weight of the vehicle, and also may increase themanufacturing cost of the vehicle.

SUMMARY OF THE INVENTION

[0009] Therefore, a need has arisen for fixed displacement compressorswhich overcome these and other shortcomings of the related art. Atechnical advantage of the present invention is that when a drive shaftis engaged, an inclination angle of a swash plate initially may be at aminimum inclination angle, and may increase to a maximum inclinationangle. Consequently, an initial frictional force between a swash plateand a shoe and an initial torque of the compressor may be reducedrelative to that of known swash plate-type, fixed displacementcompressors, as described above. As such, a vehicle's speed may notdecrease when the drive shaft is engaged.

[0010] According to an embodiment of the present invention, a fixeddisplacement compressor is described. The compressor comprises acylinder block having a plurality of cylinder bores formed therethrough,a drive shaft rotatably supported by the cylinder block, and a platerotatably mounted on the drive shaft. Moreover, an inclination angle ofthe plate varies relative to a radial line perpendicular to the driveshaft. The compressor also comprises at least one spring positionedadjacent to the plate. The at least one spring is adapted to urge theplate in a direction which reduces the inclination angle of the plate.In an embodiment, the plate is a swash plate. In another embodiment, thecompressor further comprises a cam rotor fixed to the drive shaft. Inthis latter embodiment, the at least one spring is positioned betweenthe cam rotor and the plate.

[0011] Other objects, features, and advantages of the present inventionwill be apparent to persons of ordinary skill in the art in view of thefollowing detailed description of the invention and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention, theneeds satisfied thereby, and the objects, features, and advantagesthereof, reference now is made to the following descriptions taken inconnection with the accompanying drawings.

[0013]FIG. 1 is a cross-sectional view of a swash plate-type, fixeddisplacement compressor according to an embodiment of the invention whena drive shaft is engaged.

[0014]FIG. 2 is a cross-sectional view of the swash plate-type, fixeddisplacement compressor of FIG. 1 according to an embodiment of theinvention when the drive shaft is disengaged.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention and theiradvantages may be understood by referring to FIGS. 1 and 2, likenumerals being used for like corresponding parts in the variousdrawings.

[0016] Referring to FIGS. 1 and 2, a swash plate-type, fixeddisplacement compressor 100 according to an embodiment of the presentinvention is depicted. Although the present invention is described withrespect to a swash plate-type, fixed displacement compressor, it will beunderstood by those of ordinary skill in the art that the presentinvention may be applied to swash plate-type, fixed displacementcompressors, wobble plate-type, fixed displacement compressors, or thelike. Compressor 100 may comprise a cylinder block 2, a front housing 4,a valve plate 5, and a cylinder head 8. Cylinder block 2 may besubstantially cylindrical, and also may be enclosed by front housing 4and cylinder head 8. A crank chamber 3 may be formed between cylinderblock 2 and front housing 4. Moreover, a suction chamber 6 and adischarge chamber 7 may be formed within cylinder head 8 and adjacent tovalve plate 5. An inlet port (not shown) and an outlet port (not shown)may communicate with suction chamber 6 and discharge chamber 7,respectively, and the inlet port and the outlet port may be connected toa refrigerant circuit (not shown) of an air conditioning system of avehicle. Cylinder block 2, front housing 4, valve plate 5, and cylinderhead 8 may be fixably attached to each other by a plurality of bolts 50.Compressor 100 also may comprise a plurality of cylinder bores 1 formedin cylinder block 2. Cylinder bores 1 may be arranged radially withrespect to a central axis of cylinder block 2.

[0017] Compressor 100 further may comprise a drive shaft 9, a cam rotor10, a swash plate 11, a plurality of shoes 13, and a plurality ofpistons 14. Drive shaft 9 may extend along a central axis of compressor100 through crank chamber 3 and also may be rotatably supported by fronthousing 4 and cylinder block 2 via a pair of bearings 20 a and 20 bmounted in front housing 4 and cylinder block 2, respectively.Compressor 100 also may comprise an electromagnetic clutch (not shown).A drive belt (not shown) may be used to engage the electromagneticclutch by transmitting a driving force from a crankshaft of an engine ofa vehicle (not shown) to the electromagnetic clutch. When theelectromagnetic clutch is engaged, the driving force also is transmittedfrom the electromagnetic clutch to drive shaft 9. Moreover, cam rotor 10may be fixed to drive shaft 9 and may be positioned within crank chamber3, and a slot 10 a may be formed through cam rotor 10. Swash plate 11also may be positioned within crank chamber 3, and may be slidablymounted on drive shaft 9, such that an inclination angle θ of swashplate 11 may vary relative to a line which is perpendicular to driveshaft 9. Swash plate 11 may comprise a pin member 11 a which may extendtoward cam rotor 10. Pin member 11 a may be inserted into slot 10 a ofcam rotor 10, and a coil spring 12 may urge swash plate 11 away from camrotor 10. Specifically, coil spring 12 may engage drive shaft 9 and maybe positioned between cam rotor 10 and swash plate 11, such that coilspring 12 urges swash plate 11 to move in a direction which reducesinclination angle θ of swash plate 11.

[0018] Moreover, each piston 14 may be positioned within a correspondingcylinder bore 1, and pistons 14 may reciprocate independently within acorresponding cylinder bore 1. Each piston 14 also may be connected toswash plate 11 via a pair of shoes 13. Specifically, each shoe 13 maycomprise a substantially flat surface and a substantially semisphericalportion. The flat surface may be in slidable contact with swash plate11, and the semispherical portion may rotatably engage a substantiallysemispherical cavity of piston 14.

[0019] A plurality of suction ports 15 and plurality of discharge ports16 may be formed through valve plate 5 for each cylinder bore 1. Asuction reed valve 15 a may be positioned between cylinder block 2 andvalve plate 5. Suction reed valve 15 a may open and may close suctionport 15 in order to control a flow of a refrigerant from suction chamber6 to cylinder bores 1. A discharge reed valve 16 a may be positionedbetween valve plate 5 and cylinder head 8. Discharge reed valve 16 a mayopen and may close discharge port 16 in order to control a flow of therefrigerant from cylinder bores 1 to discharge chamber 7.

[0020] In operation, when the electromagnetic clutch and drive shaft 9are engaged, the driving force from the engine of the vehicle istransmitted to drive shaft 9, such that drive shaft 9, cam rotor 10, andswash plate 11 rotate substantially simultaneously about an axis ofdrive shaft 9. Specifically, the rotational movement of drive shaft 9 istransmitted to cam rotor 10, and the rotational movement of cam rotor 10is transmitted to swash plate 11 via a coupling mechanism comprisingslot 10 a and pin member 11 a, such that swash plate 11 moves back andforth in a wobbling motion. Consequently, each piston 14 reciprocateswithin its corresponding bore 1. When pistons 14 reciprocate withintheir corresponding cylinder bore 1, refrigerant gas introduced intosuction chamber 6 via the inlet port may be drawn into each cylinderbore 1 and subsequently is compressed. When the refrigerant gas iscompressed, discharge reed valve 16 a opens and the refrigerant gas isdischarged from cylinder bores 1 into discharge chamber 7. Moreover, therefrigerant gas then is discharged from discharge chamber 7 into therefrigerant circuit via the outlet port.

[0021] During operation, a compressive force is applied to pistons 14,and pistons 14 may apply a first force M1 on swash plate 11. First forceM1 may be a force which is adapted to turn pin member 11 a in aclockwise direction, such that first force M1 may urge swash plate 11 ina direction, which increases inclination angle θ of swash plate 11.Moreover, coil spring 12 may apply a second force M2 on swash plate 11.Second force M2 may be a force which is adapted to turn pin member 11 ain a counterclockwise direction, such that second force M2 may urgeswash plate 11 in a direction which decreases inclination angle θ ofswash plate 11. Nevertheless, during operation of compressor 100, firstforce M1 may be greater than second force M2. Consequently, as shown inFIG. 1, during operation, inclination angle θ of swash plate 11 mayincrease to a maximum inclination angle, and a stroke of each piston 14also may increase to a maximum piston stroke. In contrast, as shown inFIG. 2, when compressor 100 is not in operation, first force M1 may bezero, such that only second force M2 may act on swash plate 11.Consequently, inclination angle θ of swash plate 11 may decrease to aminimum inclination angle, and the stroke of each piston 14 may decreaseto a minimum piston stroke.

[0022] When drive shaft 9 is engaged, because inclination angle θ ofswash plate 11 initially may be at the minimum inclination angle, aninitial frictional force between swash plate 11 and shoes 13 and aninitial torque of compressor 100 each may be reduced relative to knownswash plate-type, fixed displacement compressors. As such, the vehicle'sspeed may not decrease when drive shaft 9 is engaged. Moreover, afterdrive shaft 9 is engaged, first force M1 may increase and may becomegreater than second force M2, such that inclination angle θ of swashplate 11 increases until inclination angle θ of swash plate 11 reachesthe maximum inclination angle.

[0023] While the invention has been described in connection withpreferred embodiments, it will be understood by those of ordinary skillin the art that other variations and modifications of the preferredembodiments described above may be made without departing from the scopeof the invention. Other embodiments will be apparent to those ofordinary skill in the art from a consideration of the specification orpractice of the invention disclosed herein.

What is claimed is:
 1. A fixed displacement compressor comprising: acylinder block having a plurality of cylinder bores formed therethrough;a drive shaft rotatably supported by said cylinder block; a platerotatably mounted on said drive shaft, wherein an inclination angle ofsaid plate varies relative to a radial line perpendicular to said driveshaft; and at least one spring positioned adjacent to said plate,wherein said spring is adapted to urge said plate in a direction whichreduces said inclination angle of said plate.
 2. The compressor of claim1, wherein said plate is a swash plate.
 3. The compressor of claim 1,wherein when said drive shaft is engaged, said inclination angleincreases from a minimum inclination angle to a maximum inclinationangle.
 4. The compressor of claim 1, wherein when said drive shaft isdisengaged, said inclination angle deceases from a maximum inclinationangle to a minimum inclination angle.
 5. The compressor of claim 1,further comprising a cam rotor fixed to said drive shaft, wherein saidat least one spring is positioned between said cam rotor and said plate.6. The compressor of claim 5, wherein said plate is a swash plate.